The Holy See (Latin: Sancta Sedes) is the episcopal jurisdiction of the Catholic Church in Rome, in which its Bishop is commonly known as the Pope. It is the preeminent episcopal see of the Catholic Church, forming the central government of the Church. As such, diplomatically, and in other spheres the Holy See acts and speaks for the whole Catholic Church. It is also recognized by other subjects of international law as a sovereign entity, headed by the Pope, with which diplomatic relations can be maintained.
Although it is often referred to by the term “the Vatican”, the Holy See is not the same entity as the Vatican City State, which came into existence only in 1929, while the Holy See, the episcopal see of Rome, dates back to early Christian times. Ambassadors are officially accredited not to the Vatican City State but to “the Holy See”, and papal representatives to states and international organizations are recognized as representing the Holy See, not the Vatican City State.
While all episcopal sees are “holy”, the expression “the Holy See” (without further specification) is normally used in international relations, as a metonym, (as well as in the canon law of the Catholic Church) to refer to the See of Rome viewed as the central government of the Catholic Church.
The website of the British Foreign and Commonwealth Office speaks of Vatican City as the “capital” of the Holy See, although it compares the legal personality of the Holy See to that of the Crown in Christian monarchies and declares that the Holy See and the state of Vatican City are two international identities. It also distinguishes between the employees of the Holy See (2,750 working in the Roman Curia with another 333 working in the Holy See’s diplomatic missions abroad) and the 1,909 employees of the state. The British Ambassador to the Holy See uses more precise language, saying that the Holy See “is not the same as the Vatican City State. … (It) is the universal government of the Catholic Church and operates from the Vatican City State.” This agrees exactly with the expression used by the website of the United States Department of States, in giving information on both the Holy See and the Vatican City State: it too says that the Holy See “operates from the Vatican City State”.